1.Field of the Invention
The present invention concerns estimating transmission quality in a mobile radio system and in particular a device for making decisions by estimating the Viterbi algorithm in a mobile radio system.
2. Description of the Prior Art
In GSM or DCS mobile radio systems previous data and the Viterbi algorithm are used for decoding received data information and/or equalization. A description of this algorithm and the associated processing can be found in the article "The Viterbi algorithm" published in Proceedings of the IEEE, vol 61, No 3, March 1973, pages 268-278.
The problem with using the Viterbi algorithm is estimating the quality of the result because the determination of a received symbol is based on the calculation of the best path linking the received symbols during a predetermined number of baud times, the various possible paths being associated with cumulative mathematical magnitudes call metrics. Estimating the quality of the result obtained therefore entails comparing the total metric of the best path to a predetermined threshold. If the value of the metric is above the threshold the quality is deemed to be good; otherwise the quality is deemed to be bad.
Estimating the quality of the result of the Viterbi algorithm is useful for making various decisions, for example a decision to adjust the transmission power or to change cell.
Unfortunately, calculating the metric for the best path gives no information on local differences between the best path and the possible path, and these can be major differences.
For this reason the object of the invention is to provide a device for estimating the quality of the Viterbi algorithm used by a mobile radio network terminal so that it can be supplied to a decision unit of the system to modify therein one or more transmission parameters.